Process for treating a mixture of saturated and unsaturated fatty acids with expanded urea



PROCESS FOR TREATING A MIXTURE 0F SATURATED AND UNSATURATED FATTY ACIDSWITH EXPANDED UREA Filed Sept.. 30, 1952 y 1 5 L. ROSENSTEIN HAL 00,466

COTTONSEED OIL FAT TY ACIDS REACTOR REACTOR STILL; STILL. STILL.

SATURATED OLEIC LINOLEIC- LINOLENIC FATTY ACIDS ACID I ACIDS IN V ENTORS:

United States Patent G Ludwig Rosenstein and Manuel H. Gorin, SanFrancisco, Calif.

Application September 30, 1952, Serial No. 312,220 1 Claim. (Cl.26096.5)

This is a continuation-in-part of our application Serial No. 152,179filed March 27, 1950, now abandoned.

This invention refers to the fractionation of high molecular weightstraight chain fatty acids.

High molecular weight straight chain fatty acids can react with urea toform solid-phases which are stable at one temperature and can bedecomposed at another, higher temperature, liberating the fatty acidsand leaving solid urea. Moreover, the stability and ease of formation ofthese solid compounds varies with the molecular weight of the fattyacids and With the degree of unsaturation. In general, the higher themolecular weight, the more stable and more easily formed are the solidcompounds with urea. Also, the greater the number of double bonds, theless stable and the more difdcult to form are the solid compounds.

Ordinary urea reacts far too slowly with fatty acids for practicalpurposes. The addition of liquids other than water, which are solventsfor urea, accelerate the action to a practical point. 1

We have found that we can produce a certain new type of urea which willreact rapidly with the high molecular weight fatty acids to form solidswithout the aid of an accelerator. We name this new type of ureaexpanded urea, and will give directions for its production, and evidencethat it differs fundamentally from ordinary urea, and not merely by itsstate of fineness.

We have further found that the fatty acids contained in solidcombination with urea can be readily recovered by contacting the solidsWith a liquid which is a solvent for the fatty acids but not for urea,and then raising the temperature; such a solvent is referred to hereinand in the claim as a neutral solvent. Different fatty acids form sohdshaving different decomposition temperatures, and advantage can be takenof this as another means of achieving selection. In no case must thetemperature attain the melting point of the urea present.

Assuming for the moment that we have an expanded urea as thus fardefined, we will describe a process of separation as applied to acommercial material, namely cottonseed oil fatty acids; by way ofillustration, cottonseed oil fatty acids having approximately thecomposition:

. Percent Saturated fatty acids (stearic, palmitic acid, etc.) 33Unsaturated fatty acids:

Oleic acid 2 3 Linoleic and Linolenic acid 44 67 were dissolved inhexane to make a 40% solution by weight. Either stronger or weakersolutions might be used, and the 40% strength was chosen because thisparticular sample of fatty acid gives a low enough viscosity at thisconcentration to allow easy handling.

We have found that approximately 1250 pounds of expanded urea isrequired to combine with the saturated fatty acids in 1,000 pounds ofcottonseed oil fatty acids, and about 850 pounds to combine with theoleic acid therein.

The operation will be explained in conjunction with the apparatus shownin the accompanying drawing which is a diagrammatic representation ofsuitable apparatus.

Referring to the drawing, we have indicated reaction vessels 1 and 2having an inlet pipe 3 at the top of vessel 1 with pipe 4 extending fromthe bottom of vessel 1 to the top of vessel 2. Pipes 5 and 9 lead,respectively, to stills 6 and 10 from vessel 2, while pipe 7 leads tostill 8 from vessel 1.

1250 pounds of an expanded urea were charged into vessel 1, and 850pounds of the same into vessel 2.

The fatty acid solution was introduced into vessel 1 through pipe 3 at arate such that its residence time in contact with the expanded urea wasapproximately 20 minutes at approximately 25 C. Flow was continued until1,000 pounds of fatty acids had been fed. The eflluent from vessel 1 wastransferred through pipe 4 to vessel 2 and the eflluent from vessel 2was taken through line 5 to a conventional still 6, wherein the hexanewas separated from the remaining fatty acids. In vessel 1, the saturatedfatty acids were largely taken up by the expanded urea along with someof the unsaturated fatty acids, while in vessel 2 the oleic acid waslargely absorbed along with the residual amounts of saturated fattyacids as well as some of the linoleic and linolenic acids. The residueissuing through line 5 was largely the linoleic and linolenic acids insolution in hexane. This solution was charged to still 6 wherein thehexane was boiled OE and the linoleic and linolenic acids fraction wasrecovered. Fatty acid feed was now cut off and the feeding of a hot,neutral solvent commenced. In the operation under discussion, 2000pounds of liquid hexane was passed at about 110 C. and 65 p. s. i. g. atan average contact time of 15 minutes through the urea in vessel 1. andthrough line 7 into a still 8, where the hexane was removed and thesaturated fatty acid fraction having an iodine number of about 34recovered as bottom. Similarly, 1500 pounds of liquid hexane was passedthrough vessel 2 under pressure at about and a contact time of about 15minutes. The eifluent from vessel 2 was delivered through line 9 to thestill 10 wherein hexane was removed and the oleic acid fraction wasrecovered. All hexane coming from the stills may be returned for use.

Expanded urea such as is left in vessel 2 is well suited to serve as thestarting expanded urea referred to in lines 48 and 49 of column 1.

The sequence of operations outlined above is particularly useful for thepurposes intended since the expanded urea formed by decomposingurea-oleic acid-solid phase at 95 C. is more reactive than that formedby decomposing the adduct of saturated fatty acids with urea at C. Afterthe described steps the system comprising the apparatus and reagents isin a different condition than at the start. Whereas the process wasbegun with an expanded urea of uniform and sufficient degree of activitythis has now been altered to a system characterized by containing inseparate vessels, expanded ureas of different degrees of reactivity. Theeffect of this change on the further operation is to enhance theselectivity; or in other words, to sharpen the fractionation. Repetitionof the described steps will therefore result in a fraction of thesaturated fatty acids containing less unsaturated fatty acids thanbefore; and in an oleic acid fraction containing less saturated fattyacids than before. The process now has become one wherein high molecularweight fatty acids in neutral solvent are contacted successively with afirst mass of expanded urea as the sole reagent to form first urea-fattyacid adduct, and then contacting the remaining fatty acids in neutralsolvent with a second mass of expanded urea as the sole reagent havingan activity greater than that of the first reactive urea to form asecond adduct.

While in this case the difference in degrees of activity of the twoseparate masses of reactive urea was produced by varying the temperatureof decomposition at a fixed the two different masses of expanded ureahave been created, we proceed as follows:

As previously described, a 40% solution by weight of the same cottonseedoil fatty acids in commercial hexane is introduced through pipe 3 intovessel '1 at a rate so that contact time with the first expanded urea isapproximately 20 minutes at 25 C. Substantially all the saturated fattyacids having from to 20 carbon atoms will be adducted by the 1250 poundsof the first expanded urea and very little of the unsaturated fattyacids will be adducted. When 1000 pounds of total fatty acids have beenthus contacted in vessel 1, the clear infiluent from this vessel istransferred through pipe 4 to vessel 2 where it is allowed to remain incontact with the second mass of expanded urea for about 20 minutes at 25C. During this time the 850 pounds of second expanded urea adducts thesmall amount of remaining saturated fatty acids, substantially all theoleic acid, and minor amounts of linoleic and linolenic acids. Theresidual hexane solution is passed through line 5 to still 6 wherehexane is removed by distillation and a residue consisting substantiallyof linoleic and linoleic acids is obtained. From the 1000 pounds of theparticular cottonseed oil fatty acids used, this residue weighs 485pounds and has an iodine number of 172, indicating that is consistssubstantially of linoleic acid with small amounts of oleic and linolenicacids. Fatty acid feed is now cut off and the feeding of a hot, neutralsolvent is commenced. In the operation under discussion, 2000 pounds ofliquid hexane is passed at about 110 C. and 65 p. s. i. g. at an averagecontact time of minutes through the adduct in vessel 1 and through line7 into a still 8, where the hexane is removed and the saturated fattyacids fraction recovered as bottoms. These bottoms from still 8 weight327 lbs, with an iodine number of 16. It consists largely of stearicacid with minor amounts of lauric, myristic, palmitic, etc. acids andwith a minor amount of unsaturated fatty acids. Similarly, 1500 poundsof liquid hexane is passed through the adduct in vessel 2 under pressureat about 95 C. and a contact time of about 15 minutes. The efiiuent fromvessel 2 is delivered through line 9 to still 10 wherein hexane isremoved and the oleic acid fraction is recovered. The bottoms from still10 weigh 184 lbs. and have an iodine number of 94. It consists largelyof oleic acid with minor amounts of linoleic acid. The content ofsaturated acids in this fraction is very small and is not determined.

While we have described the process as applied to one fatty acidmixture, we similarly have used the complexforming properties of ureaunder appropriate temperatures and times to separate the different fattyacids from rosin acids as they occur, for example, in tall-oil. Theoperations on tall-oil parallel those described except that an oleicacid fraction is adducted in vessel 1, a linoleic acid fraction invessel 2, and the unreacted residue from still 6 consists substantiallyof rosin acids, as these do not adduct with urea.

The process has been described as using hexane, but it will operateequally well with any neutral solvent. .By neutral solvent, we mean ahydrocarbon or chlorinated hydrocarbon which is a solvent for highmolecular weight fatty acids but not for urea, and which does not itselfcombine with urea to form a solid under the described conditions.Suitable neutral solvents are iso-octane, petroleum ether, benzol,toluol, cyclo-hexane, chlorinated hydrocarbons such as carbontetrachloride, methylene chloride, trichlorethylene, etc. etc.

All details of apparatus such as valves, pumps, filter media, etc. havebeen omitted from the drawing as these are well-known to those skilledin engineering and can readily be supplied. It will be noted that thenumber of separate steps can be multiplied and that various deviceswell-known to those skilled in the art can be utilized to practice theprocess continuously and utilizing either parallel flow orcountercurrent flow.

Expanded urea can be made in a number of different ways. The followingis a broad statement of the principles involved in making expanded urea.

Ordinary urea is first caused to react with a suitable high molecularweight fatty acid or suitable linear hydrocarbon and with the aid of aurea solvent other than water to form a solid phase, which is thenremoved by filtration or other convenient means and washed with aneutral solvent. It is then decomposed by suspending in a neutralsolvent and raising the temperature sufiiciently to decompose the solidphase but not melt the urea. By neutral solvent, we mean one that is notasolvent for urea, but is a solvent for the other component orcomponents of the urea-solid phase which are released upon elevation ofthe temperature. At an elevated temperature, the solid phase willseparate into its components; the urea will remain as a finely dividedsolid and the other component or components will go into solution in theneutral solvent. The solid urea is then removed, as by filtration, andmay be washed with neutral solvent. The urea so obtained is the expandedurea of this invention; it is a light and flulfy powder and will befound to be readily reactive towards certain fatty acids andhydrocarbons without the aid of any added accelerator. The followingexamples are set forth as illustrative of the preparation of expandedurea, but the invention is not limited thereto.

Example 1.Preparati0n of expanded urea with a pure fatty acid Sufficientcommercial lauric acid was dissolved in a mixture of volumes ofiso-octane andapproximately 16 volumes of anhydrous methanol, to make asolution of approximately 10% lauric acid by weight. To this,approximately 3.3 parts by weight ofordinary commercial urea were addedfor each weight unit of lauric acid. The mixture was agitated atordinary room temperature for about one hour. The solid was filtered,washed with neutral solvent and suspended in toluol; the temperature wasthen raised to the boiling point of toluol C.) and maintained for about15 minutes. The liquid phase Was removed while hot; the urea wascollected and washed with hot toluol. The filtrate from the urea can beused repeatedly to make additional batches of expanded urea.

Example 2.Preparati0n of expanded urea with a hydrocarbon Sufficientparafiin wax (M. P. 45 C.) was dissolved in a methanol-toluol mixturecontaining about 30% by volume methanol to make a 20% solution. To thiswas added 2.4 weights of urea per weight of parafiin wax. The mixturewas agitated one hour at l920 C. The solid phase was filtered, washedwith neutral solvent and then suspended in toluol. It was raised to theboiling point (110 C.) for about thirty minutes and then filtered hot.The solid phase was expanded urea, and it is of especial interest tonote that this expanded urea,'prepared by using a hydrocarbon, was alsoactive towards high molecular weight fatty acids. Conversely, we havefound that our expanded urea, prepared by using a fatty acid, will forma solid phase without the need of an accelerator, with hydrocarbonscapable of forming, under suitable and known conditions, a solid-phasewith ordinary urea.

Expanded urea can also be made by a direct precipitation of theurea-organic complex from a urea solvent which also dissolves fattyacids, and then decomposing the solid complex, as previously described.The methanol accelerator used in the two preceding examples isconvenient in that it reduces the time necessary to form the urea-fattyacid or paraffin solid phase. However, this solid phase can also beformed by a long continued contact of ordinary urea with suitable fattyacids or hydrocarbons in solution in neutral solvent. Thermal decomposition of solid-phase thus formed and suspended in neutral solventalso gives rise to expanded urea. The following example is cited to showthis.

Example 3.Preparati0n of expanded area without the use of an acceleratorA quantity of cottonseed fatty acid was dissolved in sufiicient hexaneto make a solution containing 200 grams fatty acid per litre. To 250 ml.of this solution were added 20 grams of Merck reagent urea. Thetemperature was raised to 40 .C. and the material kept well agitated ina closed vessel for approximately twelve hours. At the end of thisperiod the solid phase was removed by filtration, washed with warmhexane and finally decomposed at 110 C. with boiling toluol for a periodof fifteen minutes. The solid urea was filtered and washed with hottoluol. It was found to consist of expanded urea and capable of rapidinteraction to form solid phase with fatty acids and with linearhydrocarbons such as those occurring in paraffin wax.

It will be obvious to those skilled in the art that this process ofmaking expanded urea can be continuous and that high molecular weightfatty acids other than lauric acid, and that linear hydrocarbons otherthan parafiin wax, can be employed.

Example 4.--Urea in four different forms was used. These were:

A. Expanded urea prepared as described in Example 1.

B. Expanded urea prepared as described in Example 1 except that it wasmaintained in toluol at 110 C. for 150 minutes instead of minutes.

C. Merck reagent urea ground to an impalpable powder.

D. Merck reagent urea.

For the test substance, we used a commercial product known as .DoubleDistilled" Cottonseed Fatty Acids. This material has the followingapproximate composition:

Saturated fatty acids (stearic, palmitic acid, etc.) 33% Unsaturatedfatty acids:

Oleic acid 23% Linoleic and Linolenic acid 44%} 0 Acid number 200 Iodinenumber 105 Titer 38 C.

Solution of this material was made up in hexane to contain 50 grams per250 ml. solution; equal amounts of the four forms of urea wereintroduced into separate equal portions of the fatty acid hexanesolutions. The suspensions were kept well agitated in closed vessels atC. At various times, samples of the clear liquid were taken and the,fatty acid content thereof determined by titration with standard KOH inthe usual manner. From the results, the percent fatty acids which hadcombined was calculated. Table I gives the results:

TABLE 1.

Ex ended Expanded Ground Reagent U i ea A Urea B Urea O Urea D F. A. F.A. F. A. F. A. Elapsed to Elapsed to Elapsed to E a to Time, Solid Time,Solid Time, Solid I une, Solid minutes Phase, minute Phase, minutePhase, min Phase,

Per- Per- Per- Percent 1 cent 1 cent 1 cent 1 1 M01 percent. 2 Allowedto stand without agitation.

Certain facts are apparent from these data. In the case of expanded urea(A), prepared by 15 minute exposure to C., 33% of the fatty acids, hadreacted after 76 minutes, while neither the finely ground urea (C), northe ordinary urea (D), showed any measurable reaction. However, after along period of standing, the finely ground urea (C) reacted with 11% ofthe fatty acids, while the reagent urea (D) reacted with 2.4% of thefatty acids. These amounts were taken up by expanded urea (A) in lessthan 5 minutes. Comparing'the expanded urea (B), prepared with minutescontact at 110 C., we see that it is approximately one-sixth as reactiveas expanded urea (A), the material which had only 15 minutes thermaldecomposition, but it is still many times as reactive as the finelyground urea (C), on the basis of the time required for conversion.Further with regard to expanded urea (A): After 33% of fatty acids hadbeen adducted (corresponding to 33% saturated fatty acids present) thereaction rate becomes very slow, indicating that this expanded urea isfar more reactive toward the saturated fatty acids than toward theunsaturated.

The fact that urea with diiferent degrees of reactivity within the rangeof practical use can be prepared is of importance in the development ofprocesses for separating the components of fatty acid mixtures or ofhydrocarbons. The most reactive urea is by no means always the mostdesirable. A highly reactive urea will combine with fatty acids orhydrocarbons so fast that it is likely to set up as a solid mass and,moreover, a control of the reaction so as to achieve selectivity isalmost impossible unless the reaction time is slow enough so thatselectivity can be accomplished by limiting the time of contact. Towardsany given sample of expanded urea, the saturated fatty acids aremostreactive; the unsaturated acids with a single double bond less. so; andthe unsaturated acids with multiple double bonds least. The followingexamples additionally illustrate the achievement of a selectiveseparation of such a mixture of saturated and unsaturated fatty acids.

Example 5.-Samples of the expanded urea previously designated A and B(Table I), were brought into contact with a hexane solution ofcottonseed fatty acids (50 g. fatty acids in 250 ml. total volume) for15 minutes. The solid phase was filtered, washed with hexane and finallydecomposed with water whereby the fatty acids were liberated. Theirmelting points and amounts were determined:

Example 6.40 grams of a commercially available Double DistilledCottonseed Fatty Acids of the composition given above were dissolved in100 cc. of commercial hexane. Five 24 gram portions of an expanded urea,prepared by contacting a urea-cottonseed fatty acid complex with boilingtoluol for about 90 minutes, were added successively to this hexanesolution of cottonseed fatty acids. After each addition of expanded ureathe mixture was agitated for 30 minutes at 20 C., then filtered, washedwith hexane and evaporated at room temperature back to its originalvolume. In each case the solid phase was decomposed with water and thefatty acids extracted with benzene and recovered by evaporation of thebenzene and their titer determined. The results are given in Table II;

It is noteworthy that the reaction proceeded rapidly and gave a hightiter product of apparently nearly constant composition until about32.5% of the fatty acids were removed, after which the rate of reactionand the titer of the product dropped sharply. Since the saturated fattyacid content of the cottonseed fatty acids was 33%, it is evident thatthese acids are taken up very selectively and much more rapidly than theunsaturated acids by this particular expanded urea.

Urea B of Example was less reactive, as shown by the lesser amount offatty acids recovered, but while the less reactive urea has taken uponly approximately half as much of the fatty acids, the melting point ofthe acids taken up was 7 C. higher, indicating that in the minutes theless reactive urea had time to combine only, or nearly so, with highermelting fatty acids whereas the more reactive urea had combined withthese and as well with some having lower melting points.

While the above Examples 5 and 6 point to difierences of reactivity ofexpanded ureas achieved by changing the times of contact with hottoluol, similar differences of reactivity can be achieved by changingthe temperatures. In the latter case, however, .another phenomenon comesinto consideration. Thesolid phases formed between urea and fatty acidsor hydrocarbons have different degrees of temperature stability; inother words, different decomposition temperatures, and to achievecomplete liberation of fatty acids or hydrocarbons from a given solidphase, the decomposition temperature of the highest member must beexceeded; hence partial and selective decomposition can be achieved inthe temperature range below the decomposition temperature of the moststable adduct.

While the difference in reaction rates towards high molecular weightfatty acids of expanded urea and ordinary urea, whether finely dividedor not, are sutficient to distinguish expanded urea from ordinary urea,the ex panded form may be additionally characterized by its unusuallylow bulk-density compared with that of ordinary urea. Expanded urea has'a bulk-density of approximately 0.4-5 gram per cubic centimeter, and inany case not exceeding 0.50 gram per cubic centimeter. Ordinary urea ofeither reagent or commercial grade after grinding has a bulk-density ofapproximately 0.75 gram per cubic centimeter. No degree of grindingalters it to less than 0.70 gram per cubic centimeter. Bulk density wasmeascylinder after each addition.

ured by adding successive portions of the powder to a 50 cc. graduatedcylinder, being careful to jar and tap the When approximately 20 cc. hadbeen added, the cylinder was jarred and tapped till no further change involume occurred. The weight and volume were then recorded. The ratio ofweight to volumeis the bulk-density.

The term expanded urea" as used in this specification and in the claimdefines a light and fluffy urea having a bulk-density not exceeding 0.50gram per cubic centimeter and being capable, when used as the solereagent, of showing substantial adduct formation within one hour withsaturated fatty acids having twelve or more carbon atoms and beinglinear.

When urea combines with fatty acids, or hydrocarbons, these latterpenetrate the crystal lattice and cause it to expand, thus changing thefundamental dimensions. We believe that when the solid phase isdecomposed as described, the expanded structure is maintained. Suitablesubstances can now more readily penetrate the structure, hence thereactivity of our expanded urea. Such expandedurea loses its reactivityon long standing at ordinary temperature or more rapidly at highertemperature, and we interpret this as the gradual return of the expandedstucture to the normal structure of crystalline urea. In other words,the expanded urea is metastable and tends to return to the stable form.

The process of this invention can be employed to remove oleic andlinoleic acids from fatty acids such as those from soy bean and linseedoil, leaving behind fractions consisting of linolenic and fatty acids ofstill higher unsaturation.

We claim:

In a process for fractionating fatty acids from their solution in aneutral solvent containing saturated and unsaturated fatty acids of morethan eleven carbon atoms, the step of contacting said solution withexpanded urea in the form of a light and fluify powder having a bulkdensity not exceeding 0.5 gram per 00., as the sole reagent having ahigh degree of selectivity for, saturated fatty acids of more thaneleven carbon atoms to form an adduct with substantially only thesaturated fatty acids; said expanded urea having been made to be highlyselective for saturated fatty acids by decomposing an adduct of urea andsaturated fatty acid of more than eleven carbon atoms by heating saidadduct suspended in a neutral solvent at a temperature of about C. for atime between 90 minutes and minutes.

Fetterly Feb. 23, 1954

